1. Field of the Invention
The present invention generally relates to copy-protected optical information recording media and methods for manufacturing the same. More specifically, the present invention relates to the manufacture of an optically readable digital storage medium that protects the information stored thereon from being copied using conventional optical medium readers, such as CD and DVD laser readers, but permits reading of the information from the digital storage media by the same readers.
2. Background of the Invention
Optical data storage media (“optical media”) are media in which data is stored in an optically readable manner. Data on optical media are encoded by optical changes in one or more layers of the media. Optical data media are used to distribute, store and access large volumes of data. Formats of optical medium include read-only formats such as CD-DA (digital audio compact disc), CD-ROM (CD-read-only memory), DVD (digital versatile disc or digital video disc) media, write-once read-many times (WORM) formats such as CD-R (CD-recordable), and DVD-R (DVD-recordable), as well as rewritable formats such as found on magneto-optical (MO) discs, CD-RW (CD-rewritable), DVD-RAM (DVD-Random Access Media), DVD−RW or DVD+RW (DVD-rewritable), PD (Phase change Dual disk by Panasonic) and other phase change optical discs. Erasable, or rewritable, optical discs function in a similar manner to magneto-optical (MO) disks and can be rewritten over and over. MO discs are very robust and are geared to business applications, typically in high-capacity disk libraries.
Optical media have grown tremendously in popularity since their first introduction owing in a great deal to their high capacity for storing data as well as their open standards. For example, a commercially available magnetic floppy diskette is only capable of storing 1.44 Mb of data, whereas an optical CD-ROM of approximately the same size can have a capacity in excess of 600 MB. A DVD has a recording density which is significantly greater than a CD. For example, conventional DVD read-only discs currently have a capacity of from 4.7 GB (DVD-5, 1 side/1 layer) to 17.0 GB (DVD-18, 2 sides/2 layers), write-once DVDs a capacity of 3.95 GB (DVD-R, 1 side/1 layer) to 7.90 GB (DVD-R, 2 sides/1 layer) (newer DVD-Rs can hold up to 4.7 GB per side), and conventional rewritable DVDs of from 2.6 GB (DVD-RAM, 1 side/1 layer) to 10.4 GB (MMVF, 2 sides/1 layer). Optical discs have made great strides in replacing cassette tapes and floppy disks in the music and software industries, and significant in-roads in replacing videocassette tapes in the home video industry.
Data is stored on optical media by forming optical deformations or marks at discrete locations in one or more layers of the medium. Such deformations or marks effectuate changes in light reflectivity. To read the data on an optical medium, an optical medium player or reader is used. An optical medium player or reader conventionally shines a small spot of laser light, the “readout” spot, through the disc substrate onto the data layer containing such optical deformations or marks as the medium or laser head rotates.
In conventional “read-only” type optical media (e.g., “CD-ROM”), data is generally stored as a series of “pits” embossed with a plane of “lands”. Microscopic pits formed in the surface of the plastic medium are arranged in tracks, conventionally spaced radially from the center hub in a spiral track originating at the medium center hub and ending toward the medium's outer rim. The pitted side of the medium is coated with a reflectance layer such as a thin layer of aluminum or gold. A lacquer layer is typically coated thereon as a protective layer.
The intensity of the light reflected from a read-only medium's surface by an optical medium player or reader varies according to the presence or absence of pits along the information track. When the readout spot is over the flat part of the track more light is reflected directly from the disc than when the readout spot is over a pit. A photodetector and other electronics inside the optical medium player translate the signal from the transition points between these pits and lands caused by this variation into the 0s and 1s of the digital code representing the stored information.
A number of types of optical media are available which permit an end-user to record data on the media, such optical media generally are categorized as “writable” or “recordable,” or “rewritable.”
“Writable” or “recordable” optical media (e.g., “CD-R” discs) permit an end-user to write data permanently to the medium. Writable media are designed such that laser light in the writer apparatus causes permanent deformations or changes in the optical reflectivity of discrete areas of the data layer(s) of the medium. Numerous writable optical media are known, including those that employ a laser deformable layer in their construct upon which optically-readable areas analogous to the pits and lands found in conventional read-only optical media can be formed (See, e.g., EP-A2-0353391), those that employ a liquid-crystalline material in their data layer(s) such that irradiation with the laser beam causes permanent optical deformations in the data layer (See, e.g., U.S. Pat. No. 6,139,933 which employs such layer between two reflective layers to effect a Fabry-Perot interferometer), and those that utilize a dye that irreversibly changes state when exposed to a high power writing laser diode and maintains such state when read with a low power reading laser (so-called, WORM, write-once-read-many times, optical media).
Rewritable optical media (e.g., “CD-RW”, “DVD-RAM”, “DVD−RW”, “DVD+RW” and “PD” media) use the laser beam to cause reversible optical deformations or marks in the data layer(s), such that the data layer is capable of being written on, read, erased and rewritten on many times. Several rewritable optical media systems are known.
In one system, an optically-deformable data layer is deformed in discrete areas by the writing laser to form optical changes representative of the data, for example, pits and lands, and erased by uniformly deforming the same optically-deformable data layer, or the portion thereof wherein the data desired to be deleted is found. In another system, a photochromic material layer is used to store the data. In this system, the photochromic material reversibly changes when the material is irradiated by light possessing certain wavelengths. For example, a colorless compound may change its molecular state to a quasi-stable colored state when irradiated by ultraviolet (UV) light, yet be returned to the colorless state upon exposure to visible light. By selectively irradiating the photochromic material layer with the one wavelength to cause an optical change, and then irradiating with the other wavelength to reverse such optical change, one is permitted to write, erase, and re-write data.
Materials that change color due to a change in crystalline state have been found to be particularly useful in rewritable media. In one system, a material that is dark in the amorphous state, but bright in the crystalline state, is used to record the data. In such system, dark amorphous marks are formed utilizing a short high-power laser pulse that melts the recording material followed by quenching to temperatures below the crystalline temperature. The data formed thereby, can be erased by heating the amorphous state over a long enough period of time between the temperature of crystallization and temperature of melt to regain the crystalline state. Ternary stoichiometric compounds containing Ge, Sb and Te (e.g., Ge1Sb2Te4 Ge2Sb2Te5) are in particular known to show a large optical contrast between amorphous and crystalline phase and have acceptable melting temperatures (tcryst=about 150-200° C., tmelt=about 600° C.). Alloys of such compounds with antimony (Sb), cadmium (Cd) and tin (Sn) have also been employed in rewritable media.
In rewritable optical media control information such as address data, rotation control signal, user information etc. is generally previously recorded on the header field in the form of pre-pits.
Data may also be stored in what are referred to as fluorescent multilayer disks. In fluorescent memory storage, the data is present as local variations of fluorescent substance properties. Typically the substance is illuminated with radiation at excitation wavelength, and the fluorescence signal is registered at a different wavelength. A spectral filter is used to separate the fluorescent signal at the receiver from the noise of the excitation radiation. Data may be stored in a 3-D manner using the fluorescent principle. The two-photon approach is often utilized when the fluorescent medium is to be rewritable. In this approach a fluorescent medium containing photochromic molecules capable of existing in two isomeric forms is used. The first isomeric form is not fluorescent and has absorption bands for UV radiation, and is capable of being transferred into the second isomeric form upon the simultaneous absorption of two long wavelength photons, said second isomeric form being capable of exhibiting fluorescence.
Hybrid optical media are also known. For example, “half-and-half” discs are known wherein one portion of the disc has conventional CD-ROM pits and the other portion of the disc has a groove pressed into the disc with a dye layer thereover to form a CD-R portion. A relatively new hybrid optical media is the CD-PROM (i.e., CD programmable ROM). The CD-PROM medium combines a read-only CD-ROM format with a recordable CD-R format on one medium, but features only a single continuous groove on the medium with the entire medium coated with a dye layer. The geometry of the continuous groove of the CD-PROM medium is modulated so as to look like ROM pits to an optical reader. It also provides no dye transition issues to overcome in manufacturing.
An optical disc medium read by moving a read head generating a radiation beam in a specified path relative to the optical medium. The radiation beam is used to differentiate regions having different optical properties, such different optical properties being used to represent the data, for example, the “on” logical state being represented by a particular region. The detectable differences are converted into electrical signals, which are then converted to a format that can be conveniently manipulated by a signal processing system. For example, by setting a threshold level of reflectance, transitions between pits and lands may be detected at the point where the signal generated from the reflectance crosses a threshold level. The pits represent a 1 and lands a 0. In this manner, binary information may be read from the medium.
The vast majority of commercially-available software, video, audio, and entertainment pieces available today are recorded in read-only optical format. One reason for this is that data replication onto read-only optical formats is significantly cheaper than data replication onto writable and rewritable optical formats. Another reason is that read-only formats are less problematical from a reading reliability standpoint. For example, some CD readers/players have trouble reading CD-R media, which has a lower reflectivity, and thus requires a higher-powered reading laser, or one that is better “tuned” to a specific wavelength.
Data is conventionally written onto pre-fabricated writable and rewritable medium individually, for example, one disc at a time, using a laser. Data is conventionally stamped onto read-only media by a die molding (injection molding) process during the manufacture of the read-only medium. Today many more data-containing optical media can be manufactured by the stamping process than by the laser writing process over a set unit of time, significantly reducing the cost of such stamped read-only optical media for large quantities of optical media. The manufacturing of a stamped medium is also considerably cheaper than in fabricating a fluorescent multi-layer medium.
Interference/reflectivity type optical media comprising a read-only format are typically manufactured following a number of defined steps:
Data to be encoded on the medium is first pre-mastered (formatted) such that data can be converted into a series of laser bursts by a laser, which will be directed onto a glass master platter. The glass master platter is conventionally coated with a photoresist such that when the laser beam from the LBR (laser beam recorder) hits the glass master, a portion of the photoresist coat is “burnt” or exposed. After being exposed to the laser beam, it is cured and the photoresist in the unexposed area rinsed off. The resulting glass master is electroplated with a metal, typically Ag or Ni. The electroformed stamper medium thus formed has physical features representing the data. When large numbers of optical media of the disc-type are to be manufactured, the electroformed stamper medium is conventionally called a “father disc.” The father disc is typically used to make a mirror image “mother disc,” which is used to make a plurality of “children discs” often referred to as “stampers” in the art. Stampers are used to make production quantities of replica discs, each containing the data and tracking information that was recorded, on the glass master. If only a few discs are to be replicated (fewer than 10,000) and time or costs are to be conserved, the original “father” disc might be used as the stamper in the mold rather than creating an entire “stamper family” consisting of “father,” “mother” and “children” stampers.
The stamper is typically used in conjunction with an injection molder to produce replica media. Commercially-available injection molding machines subject the mold to a large amount of pressure by piston-driven presses, in excess of 20,000 pounds.
In the optical medium molding process, a resin is forced in through a sprue channel into a cavity within the optical tooling (mold) to form the optical medium substrate. Today most optical discs are made of optical-grade polycarbonate which is kept dry and clean to protect against reaction with moisture or other contaminants which may introduce birefringence and other problems into the disc, and which is injected into the mold in a molten state at a controlled temperature. The format of the grooves or pits is replicated in the substrate by the stamper as the cavity is filled and compressed against the stamper. After the part has sufficiently cooled, the optical tooling mold is opened and the sprue and product eject are brought forward for ejecting the formed optical medium off of the stamper. The ejected substrate is handed out by a robot arm or gravity feed to the next station in the replication line, with transport time and distance between stations giving the substrate a chance to cool and harden.
The next step after molding in the manufacture of a read-only format is to apply a layer of reflective metal to the data-bearing side of the substrate (the side with the pits and lands). This is generally accomplished by a sputtering process, where the plastic medium is placed in a vacuum chamber with a metal target, and electrons are shot at the target, bouncing individual molecules of the metal onto the medium, which attracts and holds them by static electricity. The sputtered medium is then removed from the sputtering chamber and spin-coated with a polymer, typically a UV-curable lacquer, over the metal to protect the metal layer from wear and corrosion. Spin-coating occurs when the dispenser measures out a quantity of the polymer onto the medium in the spin-coating chamber and the medium is spun rapidly to disperse the polymer evenly over its entire surface.
After spin-coating, the lacquer (when lacquer is used as the coat) is cured by exposing it to UV radiation from a lamp, and the media are visually inspected for reflectivity using a photodiode to ensure sufficient metal was deposited on the substrate in a sufficiently thick layer so as to permit every bit of data to be read accurately. Optical media that fail the visual inspection are loaded onto a reject spindle and later discarded. Those that pass are generally taken to another station for labeling or packaging. Some of the “passed” media may be spot-checked with other testing equipment for quality assurance purposes.
Optical media have greatly reduced the manufacturing costs involved in selling content such as software, video and audio works, and games, due to their small size and the relatively inexpensive amount of resources involved in their production. They have also unfortunately improved the economics of the pirate, and in some media, such as video and audio, have permitted significantly better pirated-copies to be sold to the general public than permitted with other data storage media. Media distributors report the loss of billions of dollars of potential sales due to high quality copies.
Typically, a pirate makes an optical master by extracting logic data from the optical medium, copying it onto a magnetic tape, and setting the tape on a mastering apparatus. Pirates also sometimes use CD or DVD recordable medium duplicator equipment to make copies of a distributed medium, which duplicated copies can be sold directly or used as pre-masters for creating a new glass master for replication. Hundreds of thousands of pirated optical media can be pressed from a single master with no degradation in the quality of the information stored on the optical media. As consumer demand for optical media remains high, and because such medium is easily reproduced at a low cost, counterfeiting has become prevalent.
A variety of copy protection techniques and devices have been proposed in the art to limit the unauthorized copying of optical media. Among these techniques are analog Colorstripe Protection System (CPS), CGMS, Content Scrambling System (CSS) and Digital Copy Protection System (DCPS). Analog CPS (also known as Macrovision) provides a method for protecting videotapes as well as DVDs. The implementation of Analog CPS, however, may require the installation of circuitry in every player used to read the media. Typically, when an optical medium or tape is “Macrovision Protected,” the electronic circuit sends a colorburst signal to the composite video and s-video outputs of the player resulting in imperfect copies. Unfortunately, the use of Macrovision may also adversely affect normal playback quality.
With CGMS the media may contain information dictating whether or not the contents of the media can be copied. The device that is being used to copy the media must be equipped to recognize the CGMS signal and also must respect the signal in order to prevent copying. The Content Scrambling System (CSS) provides an encryption technique to that is designed to prevent direct, bit-to-bit copying. Each player that incorporates CSS is provided with one of four hundred keys that allow the player to read the data on the media, but prevents the copying of the keys needed to decrypt the data. However, the CSS algorithm has been broken and has been disseminated over the Internet, allowing unscrupulous copyists to produce copies of encrypted optical media.
The Digital Copy Protection System (DCPS) provides a method whereby devices that are capable of copying digital media may only copy medium that is marked as copyable. Thus, the optical medium itself may be designated as uncopyable. However, for the system to be useful, the copying device must include the software that respects that “no copy” designation.
While presently available copy protection techniques make it more difficult to copy data from optical media, such techniques have not been shown to be very effective in preventing large-scale manufacture of counterfeit copies. The hardware changes necessary to effectuate many copy protection schemes simply have not been widely accepted. Nor have encryption code protection schemes been found to be fool proof in their reduction of the copying data from optical medium, as data encryption techniques are routinely cracked.
There is a need therefore for a copy-protected optical medium, which does not depend entirely on encryption codes, or special hardware to prevent the copying of the optical medium. Such optical media should also be easily and economically manufactured given the current strictures of optical medium manufacture. The copy-protected media should also be readable by the large number of existing optical medium readers or players without requiring modifications to those devices.